Bringing Up Baby with Baby Signs

Notes from reading this article

-Seems to be a socioeconomic component to signing.  No reliable estimates, but seems to be widespread among "professional class workers in university towns". (pg. 5) I wonder if there is a way to add that component into my study, since I work in a university town.
-Signing usually abandoned when hearing child starts speaking. (pg.5)
-Pretty specific to middle-class Anglo-Americans (pg. 6)
-Earlier communication has been noted, but not necessarily linguistic skills advanced, little to no research done on baby's self esteem as relates to being able to communicate earlier (p. 9-10)
-ASL or invented signs? I would prefer to do ASL as much as possible, unless the sign is difficult (ex. help)
-3 case studies done in Central Texas observing babies and baby sign.  None of the families had prior exposure to sign language, and all listed better and earlier communication as the main goal of learning to sign. (p. 13-16)
-Most signs fall into categories: labeling, politeness formulas, requests, displays of knowledge (pg. 14)
-pg. 31 sign language is left behind when speaking begins.
-31-33 may unfortunately re-emphasize misconceptions of sign language (easy, not as good as spoken language, based on spoken language rather than separate entity.)

Reviewing references and index may prove useful.